Laser apparatus for detecting the size and form of filamentary material by measuring diffracted light

ABSTRACT

A device for measuring moving filaments includes a laser whose beam is split and the split beams not blocked directed upon distinct filament portions; the light diffracting past the filaments falls upon respective optical sensors. The filament portions may be either longitudinally spaced along the same filament, angularly spaced about the same longitudinal filament position or include the moving filament and a standard. The outputs of the optical sensing means are compared and a signal is produced representative of such a comparison. An arrangement is also disclosed which employs selected energy levels within the diffraction pattern of an unsplit beam to precisely measure a moving filament.

0 United States Patent [151 3,659,950 Troll et al. 1 May 2, 1972 [s41LASER APPARATUS FOR DETECTING 3,178,995 4/1965 Hartman ..356/159 THESIZE AND FORM ()1? 3,305,688 2/1967 Lamparter ..250/219 S fig gy $Z $$SEFOREIGN PATENTS OR APPLICATIONS 211,564 1960 Austria ..356/238 [72]Inventors: John Troll, Ridgefield; Cole Baker, Strat- 375,936 4/1964Switzerland ..250/219 S ford, both of Conn.

Primary Examiner-Ronald L. Wibert [73] Amgnee: Corporation AssistantExaminer-Warren A. Sklar [22] Filed; Ju|y 14, 1969 Attorney-Sandoe,l-lopgood and Calimafde [21] App]. No.: 841,213 [57] ABSTRACT A devicefor measuring moving filaments includes a laser [52] U.S. Cl ..356/199,250/219, 356/200, whose beam is split and the split beams not blockeddirected 356/238 upon distinct filament portions; the light diffractingpast the [51] lnt.Cl. ..G0ln 21/18,G01n 21/30,G01n 21/16 filaments fallsupon respective optical sensors. The filament [58] Fleld of Search..356/199, 200, 237-239, portions may be either longitudinally spacedalong the same 356/242; 250/219 S filament, angularly spaced about thesame longitudinal filament position or include the moving filament and astandard. [56] References Cited The outputs of the optical sensing meansare compared and a signal is produced representative of such acomparison. An ar- UNITED STATES PATENTS rangement is also disclosedwhich employs selected energy levels within the diffraction pattern ofan unsplit beam to 3,193,689 7/1965 Kerr ..250/219 S UX preciselymeasure a moving filamem 3,202,043 8/1965 Galey et al. ..356/200 X3,283,162 11/1966 Quittner ..356/200 X 5 Claims, 4 Drawing FiguresPROGRAMMER 0U TPUT C IRCUIT Patented May 2, 1972 3,659,950

2 Sheets-Sheet l PROGRAMMER COMPARATOR ou-rpur CIRCUIT FIG. I

UUTPUT CIRCUIT PROGRAMMER COMPARATOR INVENTORS JOHN T'RULL F lg 2 BYc045 54mm ATTORNEYS Patented May 2, 1972 2 Sheets-Sheet 7.

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INVENTORS JOHN TROLL COLE BAKER BY QM,

A TTOR NE Y5 LASER APPARATUS FOR DETECTING THE SIZE AND FORM OFFILAMENTARY MATERIAL BY MEASURING DIFFRACTED LIGHT BACKGROUND OF THEINVENTION Conventional arrangements for precisely determining thedimensions and/or circularity of a moving filament such as wire includea variety of types.

Arrangements which require filament contact range from simple mechanicaltechniques where the wire is paced by a micrometer for a predetermineddistance to more sophisticated eddy current and capacative systems. Sucharrangements, however, where physical contact must take place betweenthe moving wire and the measuring instrument are extremely cumbersome,require frequent inspection and maintenance, and often deform the wireitself.

Non-contacting arrangements on the other hand, such as the shadow-graphmethod that projects an enlarged image onto a photoelectric array tendto be complicated and position sensitive, and lateral filament movementefiectively negatives a finite comparison or reading.

Accordingly, it is the object of this invention to provide a device forevaluating the profile of a moving filament, which is of thenon-contacting type which is not vulnerable to lateral shifts infilament position.

It is a further object of this invention to provide a measurement systemof the foregoing type which is simple and economical, both tomanufacture and maintain, and which is extremely flexible in adapting todifferent filament sizes and shapes.

SUMMARY OF THE INVENTION Briefly, the invention is predicated upon theemployment of a laser emitting a collimated light beam which in oneembodiment is split into two or more light beams directed at respectivefilament portions. Each beam is greater in cross section than thefilament portion crossing its path and, afier passing the associatedfilament portion, impinges upon an associated optical sensor which ispositioned to intercept the diffraction pattern of the laser beam. Acomparator is fed with the sensing means signals and evaluates thedesired program conditions.

In a second embodiment of the invention the difiraction pattern isitself analyzed, and nodes within a single diffraction pattern comparedas to their spacing and/or intensity. By appropriately locating sensorsa programmed response may be initiated.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will best be understood by reference to the following descriptionof embodiments of the invention taken in conjunction with theaccompanying drawings, the description of which follows.

FIG. 1 illustrates one embodiment of the invention for effectuating thecomparison of a moving filament with a standard;

FIG. 2 illustrates a second embodiment of the invention for determiningthe circularity of the moving filament; and

FIGS. 3 and 3a illustrate the relationship between photoresponsivedetectors and the diffraction energy distribution in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION The output of the laser which may,for example, be of the helium-neon type is directed to a mask 12. In itssimplat form, the mask may be constituted by an opaque plate having acentrally disposed aperture whose form and dimensions are dependent uponthe filament being measured, and the desired diffraction pattern.

For purposes of illustration, the filament under consideration is chosento be wire of circular cross section. In such a case, it has been foundpreferable to make the mask aperture 12 also circular and of a diameterapproximately twice that of the filament. The naturally collimated lightbeam 14, which represents the unmasked output of the laser beam, isdirected to beam splitter 16 which functions to divide light beam 14intensity-wise into two beams 18 and 19. Beam splitter 16 may be simplyconstituted by a semi-transparent (half-silvered) mirror.

The reflected portion of the beam 18 is directed by virtue of theangular attitude of mirror 16 to intercept the moving filament 20 whichis maintained in reasonably close lateral tolerance by means of guides22 and 24. It will be appreciated by those skilled in the art that thedimensions shown are for purposes of illustration, and do not reflectactual linear dimensions or spacings. Suflice it to say, however,because of the collimated nature of the laser beam the spacing betweenthe beam splitter and reflectors and the filament under considerationmay vary considerably, and little loss is occasioned by separations ofseveral feet.

The transmitted split beam 19 is directed to reflector 23 (for example,a micro-finished chrome plate) and by means of the angular position ofthis reflector fed across the filament standard 25 which is fixed inposition.

After passing the standing and moving filaments, the respective beamswill each project a diffraction pattern in accordance with the presentedfilament profile. Accordingly, there is provided an optical sensor 28having portions 280 and 28b positioned to intercept the respectivediflraction patterns. While the optical sensor may take many forms, wehave chosen to illustrate it as a pair of photo-cell matrices, theindividual cells of which are led to a programmer 30.

Programmer 30 may simply be constituted by a circuit which adds energylevels giving a purely quantitative or integrative response to beevaluated by comparator 31. Programmer 30 may also be a cross-connectnetwork in which the desired order of the diffraction pattern isprogrammed through to comparator 31. Thus, for example, (and this isdependent upon the sophistication of the measurement), the comparisonmay be made only between the fundamental diffraction modes, and onlythosephoto-cells which will be impinged upon by that mode would then beled to the comparator. On more complicated or higher tolerancecomparisons, several orders of diffraction nodes and their respectiveseparations may be run through the programmer and Boolean logic appliedtherein so that a single signal may be fed from each of the arrays 28aand 28b to the comparator 31.

Comparator 31, for example, is a serial differential amplifier andthreshold device which, upon a deviation from standard exceeding apredetermined threshold, will trigger output circuit 32. Output circuit32 may be employed as a control device to mark the moving filament whereit has deviated beyond the permissible limit from the standard or it maymerely trigger an annunciator which displays the difference. The use towhich the comparator signal is put, i.e., the particular output circuit,depends upon manufacturing considerations too numerous to elaborate uponand, hence, since these systems are unnecessary to an understanding ofthe invention, they will not be described further.

FIG. 2 shows an alternative arrangement where similar parts aredesignated similarly to FIG. 1. In the embodiment of FIG. 2 the beam issplit twice and the two beams directed orthogonally to the wire 20. Inthis case a comparison of the difiraction patterns which impinge uponoptical sensors 280 and 286 permit a reading of circularity. While as inthe foregoing embodiment the beam has only been split twice, it ispossible to split the beam any number of times directing each of thebeams in a manner which will produce the desired function analysis.Thus, for example, when a circularity to extremely close tolerances isnecessary, five beams could be directed upon the wire, each emanatingfrom the same source and each impinging upon a respective optical sensorwhose outputs run through a programmer to a comparator. Naturally, theprogramming requirements would become more complex with the greaternumber of difiraction patterns which would be analyzed. Where theprogrammer size becomes impractical due to its sophistication, theoptical sensing means can take the form of a vidicon which scans theplate upon which the defraction pattern impinges. The comparator wouldthen include a stored signal (for example on magnetic tape)representative of the vidicon signal of a standard refraction pattern.The comparison would then be effected serially.

It will be appreciated that since the laser beam has a high energy levelper small cross section and is almost perfectly collimated, the beam canbe split a great number of times and reflected with no appreciable lossof definition. The diffraction patterns in the coherent beam are notsensitive to the length of the optical path and will remain distinctiveeven when projected several feet. Further, it will be appreciated thatthe described system is extremely flexible, and the difiraction may becontrolled the desired degree, dependent upon the shape of the maskingaperture, its size, and the profile of the filament (which could besquare, flat, round, etc.).

FIGS. 3 and 3a show a still further embodiment of this invention. Inthis embodiment the beam is unsplit and is positioned so as to impingedirectly upon the wire 20. As before, the wire is perpendicular to thelaser beam and is of smaller cross section than the laser beam diameter.The resultant phenomenon is equivalent to that produced by theinterference pattern of diffracted light passing through an unobstructedslit equal to the wire diameter.

As in the classic case of diffraction of light by a slit, the lightdiffracted by the small diameter wire projects an image of thefundamental laser beam plus the nodes produced by the interference oftwo diffracted patterns from the wire edges. It will be appreciated thatwhat is being observed now merely expands upon the result achieved inFIGS. 1 and 2. However, in these figures, the emphasis was uponquantitative rather than qualitative evaluation of the energydistribution.

FIG. 3 is a graph of the illumination energy or nodes produced on oneside of center. The other side is a mirror image. In a typical caseusing a 0.08 inch diameter laser beam and a 0.001 inch wire, and adistance from the wire to projection screen of 50 inches, the node tonode separation is approximately 1 inch. If a 0.0005 inch wire is used,the node separation becomes approximately 2 inches.

Superimposed on FIG. 3 is one embodiment of the node position detectionsystem utilizing the characteristics peculiar to the energydistribution. A pair of photo-sensitive detectors 40 and 41 are disposedso as to be located respectively upon the forward slope of one curve andthe rear slope of the adjacent curve. By employing this positioning, anyvariation in wire diameter will result in a movement of the curve leftor right. If the detectors are arranged as shown in FIG. 30,backto-back, so that a null is effected, any change will be doublyapparent, i.e., the movement will have twice the influence on the nulldetecting instrument.

The foregoing arrangement has the advantage that all variations inambient light, laser output, detector signal or amplifier gain, haslittle or no effect on the output signal since both detectors areequally affected.

The invention has been found to produce useful information ofdifferences as small as 50 microns in wire sizes as small as 0.0003inch.

While the principles of the invention have been described in connectionwith specific apparatus, it is to be clearly undelstood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention as set forth herein. For example, while alaser source is preferred, any source of collimated mono-frequencyelectromagnetic energy which is of a length which is short (for example,20 percent or less) with respect to the diameter size of the wire may beemployed.

What is claimed is:

l. A measurement device for the profile of a moving filament comprising:

means for emitting a collimated light beam;

a beam splitter disposed to intercept said beam and provide at least twosubstantiallgeequal light beams; means for directing said amsrespectively on at least two supported filament portions, each of saidbeams being greater in cross section than the said filament portions,each beam coacting with said associated supported filament portion toproduce a light diffraction pattern;

at least two optical sensing means, each positioned to intercept thediflraction pattern of the light passing said filament portions atdiscrete spaced positions distinct from the optical paths of said lightbeams; and

means coupled to said optical sensing means for comparing the outputsthereof and emitting a signal representative of said comparison.

2. The measurement device claimed in claim 1, further comprising astandard filament forming one of said filament portions, and a segmentof a filament under test comprising another of said filament portions.

3. The measurement device claimed in claim I, further comprising asegment of a filament under test, wherein said portions are differentangular profiles at the same longitudinal position of the filamentsegment of said filament under test.

4. The measurement device claimed in claim 1, wherein said lightemitting means for emitting a collimated light beam includes a maskhaving a circular aperture therein approximately twice the diameter ofthe filament being measured.

5. A measurement device for the profile of a moving filament comprising:

means for emitting a collimated light beam of a wavelength shortcompared to the diameter of the filament to be measured, said light beambeing directed substantially perpendicular to the axis of said filamentand being greater in diameter than said filament diameter;

means for supporting said filament;

at least two spaced, discrete optical sensing means, each positioneddistinct from the optical path of said light beam to intercept specificenergy points on specific nodes of the diffraction pattern of the lightpassing the filament; and

detector means coupled to said sensing means to efiectively provide nooutput when the profile of the moving filament is of predetermined size.

"units A.

1. A measurement device for the profile of a moving filament comprising:means for emitting a collimated light beam; a beam splitter disposed tointercept said beam and provide at least two substantially equalcollimated light beams; means for directing said beams respectively onat least two supported filament portions, each of said beams beinggreater in cross section than the said filament portions, each beamcoacting with said associated supported filament portion to produce alight diffraction pattern; at least two optical sensing means, eachpositioned to intercept the diffraction pattern of the light passingsaid filament portions at discrete spaced positions distinct from theoptical paths of said light beams; and means coupled to said opticalsensing means for comparing the outputs thereof and emitting a signalrepresentative of said comparison.
 2. The measurement device claimed inclaim 1, further comprising a standard filament forming one of saidfilament portions, and a segment of a filament under test comprisinganother of said filament portions.
 3. The measurement device claimed inclaim 1, further comprising a segment of a filament under test, whereinsaid portions are different angular profiles at the same longitudinalposition of the filament segment of said filament under test.
 4. Themeasurement device claimed in claim 1, wherein said light emitting meansfor emitting a collimated light beam includes a mask having a circularaperture therein approximately twice the diameter of the filament beingmeasured.
 5. A measurement device for the profile of a moving filamentcomprising: means for emitting a collimated light beam of a wavelengthshort compared to the diameter of the filament to be measured, saidlight beam being directed substantially perpendicular to the axis ofsaid filament and being greater in diameter than said filament diameter;means for supporting said filament; at least two spaced, discreteoptical sensing means, each positioned distinct from the optical path ofsaid light beam to intercept specific energy points on specific nodes ofthe diffraction pattern of the light passing the filament; and detectormeans coupled to said sensing means to effectively provide no outputwhen the profile of the moving filament is of predetermined size.